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How dinosaurs became birds

Ben Creisler

A new paper in Science:

Michael S. Y. Lee, Andrea Cau, Darren Naish, and Gareth J. Dyke (2014)
Sustained miniaturization and anatomical innovation in the dinosaurian
ancestors of birds.
Science  345(6196): 562-566
DOI: 10.1126/science.1252243

Recent discoveries have highlighted the dramatic evolutionary
transformation of massive, ground-dwelling theropod dinosaurs into
light, volant birds. Here, we apply Bayesian approaches (originally
developed for inferring geographic spread and rates of molecular
evolution in viruses) in a different context: to infer size changes
and rates of anatomical innovation (across up to 1549 skeletal
characters) in fossils. These approaches identify two drivers
underlying the dinosaur-bird transition. The theropod lineage directly
ancestral to birds undergoes sustained miniaturization across 50
million years and at least 12 consecutive branches (internodes) and
evolves skeletal adaptations four times faster than other dinosaurs.
The distinct, prolonged phase of miniaturization along the bird stem
would have facilitated the evolution of many novelties associated with
small body size, such as reorientation of body mass, increased aerial
ability, and paedomorphic skulls with reduced snouts but enlarged eyes
and brains.

Michael J. Benton (2014)
How birds became birds.
Science 345(6196): 508-509
DOI: 10.1126/science.1257633

Birds evolved from dinosaurs, but how long did this evolutionary
transition take? Twenty years ago, it was widely assumed that the
first bird—Archaeopteryx, which lived in the Late Jurassic (see the
photo)—evolved its feathers, wings, and ability to fly within just 10
million years or so. Since then, it has become clear that most of the
30 or more characteristics that distinguished the small, flying
Archaeopteryx from ground-dwelling, carnivorous dinosaurs (theropods)
emerged much earlier. On page 562 of this issue, Lee et al. (1)
provide evidence for sustained miniaturization for 50 million years
before Archaeopteryx evolved (see the graph).


Tetrapod Zoology blog


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